Already more than 8.6 million smart meters have been installed across Great Britain since the national roll-out began in 2015. By 2020, the Government wants to see over 50 million of them in people's homes to save people money and reduce waste. But some MPs have criticised this deadline, saying it is unrealistic, and with the National Audit Office announcing a review of the roll out, are they as good as they seem?

If you're yet to decide whether you want one, or want to find out if yours is helping you save, here’s what you need to know:

What is a smart meter?
A smart meter is made up of two parts: first, the gas and electricity meter, which replaces your existing meters, and a portable mini screen, known as in-home display (IHD). The IHD gives you visibility of your energy use in both kilowatt hours and in pounds and pence, so you can see when you're using more than you should be.

The other ‘smart’ thing about these meters is that the energy companies can read this data remotely, so they can get accurate readings of your meter easily.

Why bother with a smart meter?
The Government estimates that the average household will save £23 a year by 2020. That isn't a huge amount, but the benefit is also in having more accurate energy bills, an end to manual meter readings and fewer customer service issues are a good incentive for a start.

However, as some companies prefer you to pay via annual plans, the monthly cost is still an estimation, and some customers have complained of wrong readings. Plus, some think it can be a postcode lottery: according to The Telegraph, if you live in an area with poor signal, the meter won't be able to send readings to your supplier, meaning you will have to take the readings yourself.

But being able to see how much you are spending in relative terms can mean that you can get more of a handle on usage. You might be more inclined to turn off all the lights, or only set off the dishwasher when it's truly full, if you can see how much it costs. According to Smart Energy GB, 80% of people with smart meters have taken steps to reduce energy waste.

What about switching?
Customers can experience problems with smart meters when switching suppliers in order to save money. Smart meters can 'go dumb' and stop recording data, and you may need to go back to taking readings until the new energy company reinstall one that they can work with. If you already have a smart meter don't let this stop you from switching: you can save hundreds by shopping around, and Smart Energy insists that meters will eventually re-connect to the network.

How much will it cost?
The energy companies have to have offered every household free installation by 2020 meaning you won’t have to pay any upfront costs; however, these costs will eventually be recouped against your energy bill.

What do I need to do?
You can wait for your energy company to get in touch to arrange a suitable time and date for your smart meter to be installed. Or, ask your supplier for them to fit one if it has been rolled out in your area. If they aren't available where you live, you can register your interest which may show a demand for them to be rolled out quicker.

It will typically only take a couple of hours to install a new smart meter, depending on where your existing meters are located. Make sure the energy company takes you through how to read and use it properly.